The present invention relates generally to inkjet printers, and more particularly to an improved inkjet printhead structure.
In contrast to many other types of printers, inkjet printers provide fast, high resolution, black-and-white and color printing on a wide variety of media and at a relatively low cost. As a result, inkjet printers have become one of the most popular types of printers for both consumer and business applications. Nevertheless, inkjet technology must continuously advance to keep pace with ever-increasing customer demands for printers that print faster, at a higher resolution, and at a lower cost.
One of the more important components of an inkjet printer is the inkjet printhead. Often housed in, or mounted on, a replaceable ink cartridge, the inkjet printhead controls the application of ink to the printing medium (e.g., paper). Generally, inkjet printheads include a plurality of ink ejection mechanisms formed on a substrate. Each ink ejection mechanism includes a firing chamber with at least one ejection orifice. Each ink ejection mechanism also includes one or more firing resistors located in the firing chamber. The substrate is connected to an ink cartridge or other ink supply. Channel structures formed on the substrate direct the ink from the ink supply to the firing chambers. Control circuitry, located on the substrate and/or remote from the substrate, supplies current to the firing resistors in selected firing chambers. The ink within the selected chambers is super-heated by the firing resistors, causing the ink to be ejected through the chamber orifice toward the printing medium in the form of an ink droplet.
Conventional inkjet cartridges and printheads are well known to those of skill in the art and therefore are not described in more detail herein. Several exemplary printhead configurations are described in the following U.S. Patents, the disclosures of which are herein incorporated by reference: U.S. Pat. No. 5,636,441 to Meyer et al., entitled xe2x80x9cMethod of Forming a Heating Element for a Printheadxe2x80x9d; U.S. Pat. No. 5,682,188 to Meyer et al., entitled xe2x80x9cPrinthead with Unpassivated Heater Resistors Having Increased Resistancexe2x80x9d; and U.S. Pat. No. 6,155,675 to Nice et al., entitled xe2x80x9cPrinthead Structure and Method for Producing the Same.xe2x80x9d Inkjet printheads are typically manufactured using standard semiconductor processing methods such as are known to those of skill in the art and described in the above-referenced patents.
One problem that occurs in conventional printhead structures is damage caused to the firing resistors when a portion of an ink droplet breaks away and collapses back into the chamber and onto the resistor. Several approaches have been developed to alleviate this problem. For example, one approach involves forming the firing resistors of thicker layers that are less vulnerable to mechanical stress and impact. Another approach involves forming a protective layer over the resistors to absorb the impact. However, both approaches increase the thermal mass which must be heated to eject the ink, thereby decreasing the thermal efficiency of the ink ejection mechanism. As a result, the delay times between consecutive firings of the ejection mechanisms must be increased, thereby reducing the maximum printing speed of the printhead. Furthermore, additional protective layers increase the complexity and cost of manufacturing the printheads.
The present invention provides an improved inkjet printhead assembly adapted to reduce and/or withstand the collapse of ink back into the firing chambers. In one embodiment, the printhead assembly includes one or more firing chambers disposed on a porous substrate. An ink supply is connected to the substrate so that ink is allowed to flow through the pores of the substrate from the ink supply to the firing chamber. Thus, a substantial amount of the energy created by the impact of ink collapsing back into the firing chamber is expended within the pores of the substrate. In another embodiment, one or more firing resistors are formed in each firing chamber, and disposed adjacent the periphery of the firing chamber out of the direct impact path of collapsing ink. The peripheral firing resistors may be formed on either a porous or non-porous substrate.